By BBC News Online science editor Dr David Whitehouse

The space shuttle Endeavour's crew have finished their Earth-mapping expedition. They were allowed an extra day of observations, giving scientists more data than they had expected a week ago.

As they attempt to pull in their 60-metre (197-foot) radar mast, they will have surveyed three-quarters of the world's terrain.

By the end of the mission, some 113 million square kilometres (43.5 million square miles) will have been mapped at least twice. Scientists say that double imaging is needed to create precise 3-D maps of the Earth's topography as far north as Alaska and as far south as the tip of South America.

The United States Defense Department has said it will use the maps to improve its missile aiming and deployment of troops. Civilian users will have to settle for less precise data because of national security issues, but scientists say the information still will be far superior to what is currently available.

"There's every reason to be excited," said mission scientist Dr Thomas Hennig.

Fuel conservation

The astronauts would have mapped 6.5 million square kilometres (2.5 million square miles) more if a thruster had not malfunctioned on the end of the radar mast, the longest rigid structure ever flown in space. A weeklong effort to conserve fuel aboard Endeavour allowed the astronauts to continue mapping on Sunday and bought an additional nine hours and 10 minutes for the mission.

To squeeze out the maximum time for mapping Nasa gave up the possibility of sending two astronauts on an emergency spacewalk to crank in the mast if it were to jam. That means the mast will have to be dumped overboard if it does not retract.

When they land, the astronauts will have collected enough data to fill 20,600 compact discs. It will take scientists one to two years to go through it all.

The crew is set to shut down the radar today after taking a final look at Australia.

The landing is scheduled for 1552 CET (21:52 GMT) at the Kennedy Space Center.